Traditionally, objects such as inventory of commercial products have been given an associated identifier to allow the object to be tracked, identified, and/or monitored. Recently, barcodes are in some cases becoming displaced by RFID technology as a means for providing such identifiers. RFID technology is beneficial as it can provide an automated identification system rather than requiring a user or machine to locate the barcode tag and then scan the barcode in a particular way.
RFID technology relies on the storage and remote retrieval of data from devices typically referred to as RFID tags or RFID transponders (hereinafter commonly referred to as “RFID tags” for clarity). An RFID tag is an object that can be attached to or incorporated into a product (or even a living being such as an animal), for the purpose of providing identification of the product or information related thereto, using radio waves. There are chip-based RFID tags containing a silicon chip and a antenna and, currently, RFID tags are either passive or active.
Passive RFID tags require no internal power source. The relatively small electrical current induced in the antenna by the incoming radio frequency signal provides enough power for the circuit in the tag to power up and transmit a response. Often, passive tags signal by backscattering the carrier signal from the reader and thus the antenna is designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. Without requiring an onboard power supply, passive RFID tags can be smaller and more cost effective to implement.
Active RFID tags have their own internal power source which is used to power any circuit residing on the tag that generates an outgoing signal. Active tags have been found to be more reliable than passive RFID tags since active tags can conduct a “session” with a reader. Using an onboard power supply, an active RFID tag can transmit a higher power signal which allows them to be more effective in areas where RE signals have trouble transmitting, e.g. through water, and/or over relatively long distances. The onboard power supply also requires more space and thus active RFID tags are generally larger and more expensive than passive RFID tags.
An RFID system generally comprises one or more tags, one or more tag readers, and often other supporting infrastructure such as a database. Often, the purpose of an RFID system is to enable data on an RFID tag to be read and processed by an RFID reader. The amount of processing and the nature of the data is largely dependent on the application. For example, the information transmitted by the tag may provide identification or location information, or specifics about the object to which the tag is affixed. In typical applications such as inventory tracking, the RFID system may use small, inexpensive tags affixed to objects that are being tracked. The tag contains a transponder with a memory that is given a unique code (e.g. a product code). A signal is emitted from the reader, the signal activating the RFID tag such that the reader can read and write data to the tag. When the RFID tag passes through an electromagnetic zone created by the emission, the tag detects the reader's activation signal. The reader decodes the data encoded in the tag's memory and the data is passed to the supporting infrastructure for its particular use.
RFID technology is becoming more popular not only because it can reduce the effort involved in tracking inventory and commercial products, but also for its ability to be applied to various wider applications, such as security, access control, and electronic commerce (e.g. for securing millions of transactions in rapid, near-field payment systems). These systems typically utilize a cryptographically enabled RFID tag, such as that available from Texas Instruments and commonly referred to as a “Digital Signal Transponder” (DST). The DST is a passive RFID tag which uses an encryption algorithm, sometimes referred to as a cipher, to implement a challenge-response authentication protocol. Each DST contains a secret 40 bit encryption key, which is shared with the reader. The reader issues a 40-bit challenge, which is enciphered by the DST using the shared key. The enciphered challenge may then be truncated by the tag to produce a 24 bit response, which is then transmitted back to the reader. The received response is compared by the reader to an expected result, computed from the same shared key, in order to authenticate the DST tag.